We will study the immune response to a mouse tumor-associated embryonic antigen which by capping experiments was found physically associated with histocompatibility-2 (H-2) antigens in the L-cell plasma membrane. Experiments will be designed to determine whether the association with H-2 prevents an immune response to the antigen when animals are immunized with tumor cells. We will also employ lactoperoxidase-catalyzed cell surface iodination to explore the biochemical properties of the antigen, which is expressed by many mouse tumors, and the nature of its association with H-2.